1. Field of the Disclosure
The technology of the disclosure relates to gradient index (GRIN) lens manufacturing configured to support GRIN lens assembly, wherein the GRIN lens assembly may mount the GRIN lens in optical plugs, receptacles and the like for facilitating optical connections.
2. Technical Background
Benefits of optical fiber include extremely wide bandwidth and low noise operation. Because of these advantages, optical fiber is increasingly being used for a variety of applications, including but not limited to broadband voice, video, and data transmission as end-users require more bandwidth. Fiber optic networks employing optical fiber are being developed and used to deliver voice, video, and data transmissions to subscribers over both private and public networks. As optical cable assemblies begin to be utilized in consumer electronic applications for allowing higher data transfer speeds between electronic devices the limitations of conventional telecommunication designs are realized. Although telecommunication fiber optic networks often include separated connection points linking optical fibers to provide “live fiber” from one connection point to another connection point using cable assemblies, the needs and environment for consumer cable assembly applications are much different. In this regard, telecommunication fiber optic equipment is located in data distribution centers, central offices, or other clean environments for supporting optical fiber interconnections and typically do not experience the large number of mating cycles like those required for consumer electronic applications. Moreover, telecommunication cable assemblies are high-precision products that are typically protected from dirt, debris, and the like; whereas, consumer electronic devices will need to operate in ordinary environments where exposure to dirt and debris will be a common occurrence.
Fiber optic connectors are provided to facilitate optical connections with optical fibers for the transfer of light and associated data. For example, optical fibers can be optically connected to another optical device, such as a light-emitting diode (LED), laser diode, or opto-electronic device for light transfer. As another example, optical fibers can be optically connected to other optical fibers through mated fiber optic connectors. In any of these cases, it is important that an end face of an optically connected optical fiber be precisely aligned with the optical device or other optical fiber to avoid or reduce coupling loss. For example, the optical fiber is disposed through a ferrule that precisely locates the optical fiber with relation to the fiber optic connector housing.
By way of example, conventional fiber optic connectors for telecommunications use a flat end-faced multi-fiber ferrules for facilitating multiple direct optical fiber-to-optical fiber connections between the fiber optic connector supporting the ferrule and other fiber optic connectors or other devices having an optical connection. In this regard, it is important that fiber optic connectors are designed to allow the end faces of the optical fibers disposed in the ferrule to be placed into contact or closely spaced with an optical connection or other optical fiber for light transfer. These conventional multi-fiber, fiber optic connectors used for the telecommunication applications require a time-consuming manufacturing process for preparing a precision surface for direct optical fiber-to-optical fiber mating. By way of example, after the optical fibers are secured so the optical fiber extends beyond the mating end face, the excess fiber is removed by laser cleaving and the remaining protruding fiber is mechanically polished using abrasives for obtaining a precision end face with a highly planar array for maintaining tight alignment of optical fibers between connectors. When these connectors are mated, the end faces of the fibers touch providing for low-loss across the optical interface, but precise polishing is required to obtain this type of mating geometry. This high precision polishing is costly and difficult since it is time-consuming requires equipment and consumables for polishing and multiple manufacturing steps. Moreover, this type of construction is not well suited for the large number of mating cycles that a consumer device application is expected to experience. Thus, conventional constructions and methods for making cable assemblies are not suitable for cable assemblies directed to consumer devices for these and other reasons.
Fiber gradient index (GRIN) rod lenses offer an alternative to costly, high accuracy mechanical polishing. FIG. 1A is an example of a GRIN lens 10. The GRIN lens may be concentric to a longitudinal axis A1 and may have a diameter D1 and length L1. The GRIN lens 10 may comprise a fiber GRIN rod lens drawn from a multimode fiber core cane.
GRIN lenses focus light through a precisely controlled radial decrease of the lens material's index of refraction from an optical axis at a longitudinal axis A1 to the edge of the lens at a radius r1 from the longitudinal axis A1. FIG. 1B depicts an exemplary decrease in an index of refraction N for the GRIN lens of FIG. 1A. As shown in FIG. 1B, the index of refraction is n2 at the center of the GRIN lens 10 (at the longitudinal axis A1) is typically the highest value and decreases to an index of refraction of n1 at the edge of the lens which is at radius r1. Exemplary indices of refraction may be 1.54 for n2 and 1.43 for n1 at a radius r1 of 0.25 millimeters, and other values are commercially available.
The internal structure of this index gradient can dramatically reduce the need for precision mechanically-polished fiber arrays and results in a simple, compact lens. This allows a GRIN lens 10 with flat surfaces to collimate (focus into infinity) light emitted from an optical fiber or to focus an incident beam into an optical fiber. For example, FIG. 1A depicts a quarter-pitch GRIN lens 10 which collimates light from a single point source P located at a first optical surface 11 of the GRIN lens 10. The collimation is shown by light rays 12(1), 12(2), 12(3), 12(4), 12(5) which exit a second optical surface 14 of the GRIN lens 10 parallel. The GRIN lens 10 may be, for example, a GRIN lens manufactured by Corning, Incorporated of Corning, N.Y.
The GRIN lens 10 can be provided in the form of a glass rod that is mounted, for example, in an optical connection such as a fiber optic connector. The flat surfaces of a GRIN lens allow easy bonding or fusing of one end to an optical fiber disposed inside the fiber optic connector with the other end of the GRIN lens disposed on a ferrule end face of the fiber optic connector. The flat surface on the end face of a GRIN lens can reduce aberrations, because the end faces can be polished to be planar or substantially planar to the end face of the ferrule. The flat surface of the GRIN lens allows for easy cleaning of end faces of the GRIN lens.
Conventional labor-intensive processes to create GRIN lenses from GRIN rods are expensive because of the complexities in processing parts that may have sub-millimeter features and precise optical surface requirements for optical performance. New approaches are needed to reduce the manufacturing cost of GRIN lenses while maintaining product quality.